The invention relates to the art of forming articles from molten glass, and more particularly to the formation of articles from sensitized photochromic glass.
When forming articles from phototropic or photochromic sheet glass such as sunglass lenses or windows for trains, busses, automobiles and the like, the temperature cycle which is required to sensitize the reversible darkening and fading properties of photochromic glass compositions subjects the glass to times and temperatures, and of course viscosities, other than those that are required to sag the sheet glass into such lenses or windows. Thus, during normal sensitizing cycles, the photochromic sheet glass had a tendency to severely distort or deform which rendered it useless for its intended purpose. Although it would be possible to hold sheets of flat photochromic glass in a verticle or upright position while they pass through the high temperature, low viscosity region required to develop the reversible photochromic properties, and then tilt them to a sagging position during the ensuing cooling cycle to bring the object down to room temperature, such a procedure would not only require extremely fine control of the temperature cycle but also the use of complex mechanisms made from special materials with high temperature capabilities, as the sheet would have a tendency to elongate and to wrinkle at its supporting points. As an alternative solution, a former with the desired final shape of the article could be used to allow the sheet of photochromic material to sag over the former during the sensitizing temperature cycle, however such a procedure has a disadvantage of impressing marks from the surface of the former on the pristine, fire-polished drawn sheet glass, thus destroying the optical quality which is of paramount importance in the use for which the lenses or windows are intended. Finally, a third method would be to sag and sensitize the articles during the same temperature cycle without deleteriously contacting anything, as suggested in U.S. Pat. No. 4,088,470, however most known photochromic glass compositions will not function in this manner for producing many products.
The present invention, however, teaches a way of obtaining a preferred method of sagging and sensitizing the photochromic glass during the same temperature cycle by laminating a molten photosensitive skin glass onto a molten higher viscosity core glass.
It thus has been an object of the present invention to improve upon the known technology of forming and sensitizing photochromic glass articles by initially laminating a skin of photosensitive glass onto a core glass of higher viscosity during the forming of such glasses into sheet, and utilizing such core glass to support the photochromic skin glass during the sensitizing cycle.